The present invention relates to a multilayered circuit board constructed by laminating a plurality of sheet members in which, for example, electrodes formed on the different sheet members via-holes. The present invention also relates to a method for producing the multilayered circuit board.
In general, a multilayered circuit board is constructed as follows. That is, for example, electrodes are formed on a surface of a green sheet (dielectric green sheet) composed of a dielectric material, via-holes filled with a conductive paste are arranged for the dielectric green sheets to conduct the electrodes between the sheets, and the plurality of dielectric green sheets are laminated and integrated into one unit by sintering them.
In the case of a conventional multilayered circuit board, when passive parts such as capacitors, coils, and resistors are mounted, the following methods are adopted: a method in which the passive parts are mounted as chip parts on the surface of the multilayered circuit board; and a method in which the passive parts are formed on the surface or at the inside of the multilayered circuit board.
It is required to realize a small size and a low price for the parts to be used for wireless communication system such as portable telephones. In the case of the method in which the chip parts are mounted on the surface of the multilayered circuit board, it is necessary to ensure a certain aerial size to mount the chip parts. Therefore, the shape of the substrate is determined by the aerial size, and there is a certain limit to realize the small size.
Description is made, for example, in Japanese Laid-Open Patent Publication No. 59-17232, in relation to the method in which the capacitors and resistors are formed on the surface or at the inside of the multilayered circuit board. In this method, a dielectric green sheet, a green sheet composed of a resistor material (resistor green sheet), and a green sheet composed of an insulator material (insulator green sheet) are previously prepared. For example, the dielectric green sheet, having a high dielectric constant, is allowed to intervene between the electrodes for constructing the capacitor. The resistor green sheet is allowed to intervene between the electrodes for constructing the resistor.
In the case of a conventional multilayered circuit board, there is no problem when a single electronic part is formed. However, the following inconvenience arises when a plurality of types of electronic parts are formed. That is, for example, when it is assumed that the capacitor and the resistor are formed in the multilayered circuit board, it is desirable that the dielectric green sheet, having a high dielectric constant, is allowed to intervene between the electrodes for constructing the capacitor, and the resistor green sheet, having a desired specific resistance, is allowed to intervene between the electrodes for constructing the resistor.
However, for example, when the capacitor and the resistor are formed in the same layer, the following inconvenience arises. That is, if the green sheet is changed so that the specific resistance of the resistor is a desired specific resistance, the green sheet, which is allowed to intervene between the electrodes for constructing the capacitor, is also changed simultaneously. Although the resistor successfully acquires the desired specific resistance, the capacitor fails to acquire a desired capacity.
When a plurality of capacitors are formed, it is necessary that all of the capacitors are arranged in the same layer, or the number of dielectric green sheets having the high dielectric constant is increased to arrange the plurality of capacitors in the different layers respectively. In the case of the former, the following problem arises. That is, the leading arrangement for the wiring is complicated, because the plurality of capacitors are formed in the same layer. As a result, the design is consequently restricted. Further, the characteristics are deteriorated, and the size is consequently increased as well, because the wiring arrangement is lengthened.
In the case of the latter, the following problem arises. That is, almost all portions of the green sheets for constructing the multilayered circuit board are occupied by the dielectric green sheets having the high specific resistance. As a result, unnecessary stray capacitance and coupling are increased, and it is impossible to obtain the desired device characteristics.
On the other hand, when the resistor is formed, the green sheet, which is positioned to intervene between the electrodes for constructing the resistor, is used after first being cut to have a necessary shape. For this reason, when a plurality of resistors having different resistance values are formed, it is necessary to cut the green sheet to have different shapes in conformity with the resistance values respectively. Therefore, the number of steps is increased.
In the case of this technique, for example, the following problem also arises. That is, the multilayered circuit board is distorted after the lamination, because the green sheet cut to have the desired shape is partially added and laminated.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a multilayered circuit board and a method for producing the same in which the characteristics of the respective electronic parts can be improved, and it is possible to realize a small size as well, although a variety of types of electronic parts are formed.
According to the present invention, a multilayered circuit board is provided, constructed by laminating a plurality of sheet members. One or more via-holes are formed in each of the sheet members respectively, and a material in conformity with a type of an electronic part is inserted into the via-holes with which the electronic part is formed.
Accordingly, for example, a material having a high dielectric constant can be inserted into a via-hole disposed at a portion for forming a capacitor. A resistor material, capable of obtaining a desired resistance value, can be inserted into a via-hole disposed at a portion for forming a resistor. A material having a high magnetic permeability can be inserted into a via-hole disposed at a portion of a coil for transmitting a magnetic flux.
Therefore, it is unnecessary to change the sheet member in order to obtain the desired characteristics for a certain electronic part. It is enough to change only the material inserted into the via-hole. That is, the formation of the electronic parts is not affected by the characteristic of the sheet member. It is possible to improve the degree of freedom of the design, and it is possible to effectively realize a small size of the multilayered circuit board.
It is unnecessary that the electronic part of the same type is formed in the same layer. Therefore, the wiring is easily formed, and the characteristics of the electronic parts can have the desired characteristics. Further, it is possible to expand the degree of freedom of the design in consideration of the wiring.
For example, when the capacitor is formed with different layers, it is enough that the material having a high dielectric constant is inserted into the via-hole disposed at the portion for forming the capacitor. Therefore, it is unnecessary to laminate multiple layers of sheet members having the high dielectric constant. It is possible to suppress the increase in unnecessary stray capacitance and coupling.
Even when a plurality of resistors having different resistance values are formed, it is unnecessary to cut and laminate each of sheet members in conformity with the resistance value. The material itself which is inserted into the via-hole disposed at the portion for forming the resistor may be selected and inserted in conformity with the desired resistance value. Therefore, it is possible to avoid any occurrence of unnecessary strain in the multilayered circuit board. Further, it is possible to realize a small size for the multilayered circuit board.
When a plurality of types of the electronic parts are formed for the multilayered circuit board constructed as described above, it is also preferable the materials in conformity with the types of the electronic parts are inserted into the via-holes for forming the plurality of types of the electronic parts respectively.
It is preferable that an insulating material is inserted into the via-hole for forming no electronic part. Accordingly, for example, when the sheet members are laminated, sintered, and integrated into one unit, unnecessary shrinkage is not caused. It is possible to obtain the multilayered circuit board approximately as designed. For example, it is preferable that a material equivalent to the sheet member is used as the insulating material.
It is also preferable that electrodes for constructing each electronic part are formed at both end surfaces of the via-holes, respectively. In this arrangement, a resistor material may be inserted into a via-hole interposed between a pair of the electrodes for constructing a resistor, or a material having a high dielectric constant may be inserted into a via-hole interposed between a pair of the electrodes for constructing a capacitor. Further, a material having a high magnetic permeability may be inserted into a via-hole located at a magnetic flux-permeating portion surrounded by electrodes for constructing a coil.
It is preferable that the via-hole is formed by means of punching out with a die. In this case, it is easy to obtain the desired dimensional accuracy, and it is easy to obtain the desired characteristics of the electronic part.
According to another aspect of the present invention, a method for producing a multilayered circuit board constructed by laminating a plurality of sheet members is provided. The method includes a via-hole-forming step of forming one or more via-holes in each of the sheet members respectively, a material-inserting step of selectively inserting a material in conformity with a specific type of electronic part into the via-hole corresponding to a portion for forming the electronic part thereafter, an electrode-forming step of forming electrodes at the necessary portions of the respective sheet members, and a step of laminating and integrating the respective sheet members into one unit.
Accordingly, it is possible to easily manufacture the multilayered circuit board in which the characteristics of respective electronic parts can be improved, and it is possible to realize a small size as well, although a variety of types of electronic parts are formed.
It is preferable that in the via-hole-forming step, the via-hole is formed by means of punching out with a die. It is also preferable that in the material-inserting step, a resistor material is selectively inserted into a via-hole which is located at a portion for forming a resistor thereafter and which is interposed between a pair of the electrodes for constructing the resistor.
It is also preferable that in the material-inserting step, a material having a high dielectric constant is selectively inserted into the via-hole which is located at a portion for forming a capacitor thereafter and which is interposed between a pair of the electrodes for constructing the capacitor. It is also preferable that in the material-inserting step, a material having a high magnetic permeability in the step of inserting materials is selectively inserted into the via-hole which is located at a portion for forming a coil thereafter and which is disposed at a portion for permeating a magnetic flux.
Further, it is preferable that in the material-inserting step, an insulating material is selectively inserted into the via-hole for forming no electronic part. For example, it is preferable that a material equivalent to the sheet member is used as the insulating material.
Of course, when the wiring is made between the multiple layers with the via-holes, a conductive material is inserted into the concerning via-holes.